The present invention relates to a method for producing decorative prints and a device for performing said method.
Carrier materials provided with a decor, as for instance wood-based boards, are typically used as flooring element or for covering walls and ceilings. In the past the wood-based boards used as carrier materials for this purpose where mostly coated with a décor paper, whereby the diversity of different pattern décor papers were and are not limited.
As an alternative for using décor papers on wood-based boards the direct printing of wood-based boards as carrier materials has been developed in the past since a printing of paper and its subsequent laminating or direct coating on the wood-based board is omitted.
The printing techniques mainly used hereby are the gravure printing process and the digital printing process. The gravure printing process is a printing technique, in which the elements to be imaged are present as deepening in a print form, which is colored before printing. The print color is especially located in the deepening and is transferred due to the contact pressure of the printing form and adhesion forces onto the object to be printed as for instance a carrier material. In contrast in case of digital printing the print image is transferred directly from a computer to a printing machine as for instance a laser printer or an ink jet printer. Thereby the use of a static print form is omitted.
In the course of the technical development of the print technology of different carrier materials the digital printing is however more and more used. While digital printing processes were at first used in particular in the graphic industries as for instance advertisement agencies, advertising material manufacturers and print shops it has been shown in the meantime that digital printing processes are also more often found in other industry branches. There are a lot of different reasons for this, wherein however two essential arguments are recognized. The digital printing allows the production of a print image with a particular high quality due to higher resolution and allows furthermore a broader application range at high flexibility.
The disadvantage of higher costs of the digital printing technology per print, in particular in comparison to conventional printing methods, as for instance the gravure printing or offset printing takes thereby more and more the backseat.
Despite the multiple advantages the technical better and more demanding digital print has also problems, which are in particular present if intentional or unintentional combinations with other printing processes occur at products.
This can cause confusions already in the first product steps, for instance when a suitable décor is out sorted or selected by a costumer. If for instance a décor is sorted out or presented at a cylinder engraver or in a design studio at first as digital print with a corresponding high resolution of for instance 600 dpi (dots per inch) and subsequently for said décor an engraved décor print cylinder for the cylinder slot provides only still a resolution of about 60 to about 80 dpi then the two prints will show significant difference in a visual comparison.
An approach for solving this problem is presented in EP 1 858 244. The method described there allows the production of the same décor on two different carrier materials using an uniform starting data set, wherein the décor is printed at first on a first carrier material as reference print with an ink jet printer in a first printing line in digital printing and parallel or subsequently the same décor is printed on a second carrier material by means of a print cylinder in a gravure printing process in a second printing line. Accordingly at least one identical digital starting data set is used for out sorting or producing a reference print by a digital printer and when engraving print cylinders.
Digital printing is carried out today almost exclusively using the color system CMYK. The CMYK color model is a subtractive color model, wherein the abbreviation CMYK stands for the three color ingredients cyan, magenta, yellow and the black component key as color depth. A color space (gamut) can be mapped with said color system, which suffices multiple requirements from different areas. In any case, the CMYK color space is a compromise, which provides that specific colors cannot be generated at all or additionally the use of additional colors is still required. This can result in color deviations, when a décor is transferred from a digital printing process to a gravure printing process even though the same data set is used for the digital print as well as for the cylinder engraving. This problem is in particular prevalent where a lot of yellow and brown colors have to be generated during printing as in the reproduction of wood décors in the furniture and laminate floor industry.
This can be counteracted by using the same pigments for the digital printer and for the gravure printing. The manufacturer of wood-based boards provided with décors is still faced with this not yet solved problem.
Furthermore, on the one hand products shall become cheaper by mass production and on the other hand a larger variety is expected by the costumer, which is mirrored for instance in an almost endless décor variety. A considerable problem is thereby a prediction, which a manufacturer for instance of decorative surfaces for consumer goods such as laminate floors has to make regarding the question which new decors are excepted by the customers and which not.
When redesigning a collection a manufacturer of decorative plates has to buy a minimum quantity of printed décor paper or printed finish films of each décor. The minimum quantity of paper is typically in the range of about one ton, what corresponds to about 15.000 m2. This décor paper has to be impregnated subsequently, to be pressed on carrier boards and further processed. If now exactly this décor is not successful on the market, remaining quantities are obtained on all value added levels, which cannot be used any further. The economical damage arising therefrom is considerable. In addition the color setting of the décor is determined at least for the one ton of paper.
A possibility to solve this problem would be the production of all decors exclusively as digital print. This however has the severe disadvantage that these decors are considerably more expensive in respect to the printing costs. Furthermore the higher quality level of the décors due to the higher resolution of the digital print could devaluate other non-digital printed decors and could thus provide a sales loss of conventional printed carrier materials.
An increasing trend is the lot size, which steadily decreases. The digital printing technology can take this trend in general into account. Due to the high flexibility of the digital print, it is possible to not only print directly paper or film webs, but also to print directly carrier boards such wood-based boards. Herewith some value added levels can be skipped on the way of further refinement to semi-finished or finished products as for instance furniture boards, laminate floors or façade boards, what provides a further flexibilisation and simplification of the production process.
A particular challenge is thereby a combination of different print processes, since until now visible differences occur in case of a desired or undesired combination of high quality digital printing in comparison to other printed processes. These differences are than often seen and claimed as quality defects.